As an increasing number of cash-strapped states turn to virtual schools — where computers replace classmates and students learn via the Internet — a new study is raising questions about their quality and oversight.

In research to be released Tuesday, scholars Kevin G. Welner and Gene V. Glass at the National Education Policy Center at the University of Colorado assert that full-time virtual schools are largely unregulated.

Once used by home-schoolers, child actors and others in need of a flexible way to learn outside a classroom, virtual schools have grown in popularity in the past several years. Cyber-schools generally operate as charters, outside the traditional system but funded with taxpayer dollars.

Nationwide, more than 200,000 students are enrolled in full-time virtual school programs, in which students have no face-to-face contact with teachers. And virtual schools are the fastest growing alternative to traditional public schools, the study found.

Supporters say they allow students to learn at their own pace and provide access to teachers and subjects that may not be available at traditional schools. Critics say they siphon resources and deprive students of socialization.

Their spread comes despite a lack of any data about their impact on children from kindergarten through high school, the researchers found. “We’re going whole hog into something that we don’t have research on,” Welner said.

Many supporters trumpet a 2009 analysis by the U.S. Education Department, which looked at published studies and concluded that online students performed “modestly better,” on average, than those getting face-to-face instruction. But the federal report compared traditional students with those who received a “hybrid” education combining online courses and face-to-face instruction, Welner and Glass said.

The lack of data on full-time virtual education far outstrips other areas of American education, Welner said in a recent interview: “Without evidentiary support, I would not say, ‘Try this out.’ You’re basically becoming a guinea pig.”

Although often embraced by policymakers as less expensive than brick-and-mortar schools, virtual schools often receive the same per-pupil funding from governments despite having a much higher student-to-teacher ratio and no costs for transportation or classrooms, the researchers said.

“Private operators are gaining access to large streams of public revenue, but the public is not getting full information on the actual costs of these programs, so it’s not clear if taxpayer money is being used properly,” Glass said.

Five for-profit companies account for most full-time virtual schools: K12, Educational Options, Apex Learning, Plato: A+LS and Connections Academy.

Welner and Glass’s suggestions include:

●Authentication: Because it’s possible for others to complete students’ work or take tests, schools should take measures to confirm identity, such as using a trusted organization to administer in-person exams.

●Accreditation: Virtual schools should be accredited by independent firms or agencies.

●Audits: States should conduct financial audits of the firms that run virtual schools to determine actual costs and whether the per-pupil payment is reasonable.